<template>
	<div class="list">
		<ul>
			<li 
			class="item"
			v-for="item of letters"
			:key="item"
			:ref="item"
			@touchstart.preventDefault="handleTouchStart"
			@touchmove="handleTouchMove"
			@touchend="handleTouchEnd"
			@click="handleClick"
			>{{item}}</li>
		</ul>
	</div>
</template>

<script>
export default {
	name:'CityAlphabet',
	props:{
		cities:Object
	},
	computed: {
		letters () {
			const letters = []
			for (let i in this.cities) {
				letters.push(i)
			}
			return letters
		}
	},
	data () {
		return {
			touchStatus: false,
			startY: 0,
			timer: null
		}
	},
	updated () {
		this.startY = this.$refs['A'][0].offsetTop
	},
	methods:{
		handleClick (e) {
			this.$emit('change',e.target.innerText)
		},
		handleTouchStart () {
			this.touchStatus = true
		},
		handleTouchMove (e) {
			if (this.touchStatus) {
				if (this.timer) {
					clearTimeout(this.timer)
				}
				this.timer = setTimeout(() => {
					const touchY = e.touches[0].clientY - 79
					const index = Math.floor((touchY - this.startY) / 20)
					if (index >= 0 && index < this.letters.length) {
						this.$emit('change', this.letters[index])
					}
				}, 50)
			}
		},
		handleTouchEnd () {
			this.touchStatus = false
		}
	}
}
</script>

<style lang="stylus" scoped>
	@import '~styles/varibles.styl'
	.list
		display flex
		flex-direction column
		justify-content center
		position absolute
		right 0
		top 1.58rem
		bottom 0
		width .4rem
		.item
			text-align center
			line-height .4rem
			color $bgColor
</style>